This is a 3 foot loop which can have many purposes but primarily for extending a 1 or 2 dog line when using on a bike.
The extra length covers the distance over the front wheel allowing for the steeper angle.
You might also need the optional loop to wrap around the stem of your bike. This avoids your karabiner making contact with the stem, thus avoiding ‘clanking’ noises that might unsettle the dog. Also you wont damage paintwork.
IMPORTANT : Do not use a gangline of any sort over the wheel of a scooter or bike without passing it through a ‘wand’ type device for holding the line away from the wheel to avoid it getting tangled in the wheel. There are several types available from other suppliers.